Collinear four-point probe head and mount for resistivity measurements

ABSTRACT

An improved resistivity probe comprised of a rigid strip of electrically nonconducting material having a number of metallic, generally parallel pins coupled thereto. The strip can be mounted in a vertically shiftable probe head in any suitable manner. In one embodiment, the pins are rigidly secured by an epoxy to the strip. In another embodiment, the probe includes a pair of rigid strips having semi-cylindrical recesses on the inner faces thereof for receiving therebetween a number of resistivity measuring pins. The strips are held together by rivets or other fasteners. A multiple probe assembly can be made with a disk-like body having a number of angularly disposed slots therethrough for receiving a number of probes with each probe including a rigid strip having a number of pins coupled thereto. The probes extend into respective slots of the body so that the pins project downwardly from the lower face of the body to permit multiple resistivity measurements to be made without having to rotate the probes. An improved mount for a resistivity probe includes an arm mounted on an upright post for up and down movement, and a moving means which can be electrical, pneumatic, hydraulic or vacuum operated, can be used raising and lowering the arm. A single probe or a multiple probe assembly can be used on the outer end of the arm for making resistivity measurements.

This invention relates to improvements in the making of resistivitymeasurements and, more particularly, to an improved resistivity probeand a mount for such a probe.

BACKGROUND OF THE INVENTION

The measurement of resistivity of semiconductor wafers is an essentialpart of the processing of such wafers. A number of different types ofprobes and probe mounts have been conventionally provided for makingsuch measurements. Typical of probes of this nature are those of thetype made and sold by Kulicke and Soffa Industries, Inc. of Horsham, Pa.and identified as Fell Resistivity Probe Head, and Kullicke and SoffaDisposable Probe Head. This company also produces the Model 3007A waferlocating resistivity probe base and the Model 5000 resistivitycalculator, the latter including mounts for the Fell and disposableprobe heads. Other companies which make mounts for probes of this typeinclude Signatone Corporation of Santa Clara, Calif. and Macronetics,Inc. of Mountain View, Calif.

For the most part, the wafer engaging pins of conventional resistivityprobes are shiftable relative to the heads which carry the probes. Anexplanation of the construction of conventional probes is set forth inthe periodical, Solid State Technology, June 1969, in an articleentitled "Mechanical Aspects of Testing Resistivity of SemiconductorMaterials and Diffused Layers," by P. P. Clerx. In this article, it ismade clear that the various pins of a probe head are shiftable relativeto each other and have individual springs which bias the pins downwardlyyet allow the pins to move upwardly when the lower ends of the pinsengage selected locations on a semiconductor wafer whose resistivity isto be measured.

While the foregoing probe heads have been suitable for a number ofdifferent applications, they require extremely high accuracy in mountingand the use of individual springs for bias forces for seriouslyaffecting their reliability so that the production costs have beenrelatively high. Since the pins experience wear and are often timeshaving to be replaced, a need for a more economical way of mounting thepins and replacement of the probe has arisen to offset production andoperational costs.

SUMMARY OF THE INVENTION

The present invention satisfies the aforesaid need by providingimprovements in the construction and mounting of probe heads forresistivity measurements. To this end, the present invention providesseveral embodiments of probe heads which can be constructed in a simplemanner and at minimum cost yet the probe heads can be quickly and easilymounted in a probe head for immediate use in taking resistivitymeasurements of semiconductor wafers.

In one embodiment of the invention, the probe includes a rigid strip ofplastic or other non-conducting material and a number of spaced,generally parallel pins secured to one side face of the strip by anadhesive, such as an epoxy. The pins project upwardly from the upperedge of the strip and downwardly from its lower edge, and the pins arepointed so that they can make point contact with a semiconductor waferduring resistivity measurements. The upper ends of the pins are providedwith collars which make electrical contact with the pins and provide themeans by which wires can be attached to the pins themselves. The rigidstrip can be shiftably secured in any suitable manner in a probe head orhousing with a height bar of rubber or the like engaging the flat upperfaces of the pins to limit upward movement of the strip and pins as aunit. One or more weight or gram loading bars can be coupled with theprobe to provide specific loading for the pins. Such loading willprovide the necessary control and accuracy needed to make resistivitymeasurements.

Another embodiment of the probe of this invention includes a pair ofrigid strips having semi-cylindrical recesses on their inner surfaces sothat the pins can be received in the recesses and slightly movablebetween the strips to form a probe that can be mounted in a probe headas mentioned above with respect to the first-mentioned probe, yet theprobe unit can be used with gram loading bars for the previouslymentioned purpose.

A multiple probe assembly can be formed from a disk-like body having anumber of angularly disposed slots therethrough located about thecentral axis of the body. The slots receive respective probes of one ofthe types mentioned above so that the pins of the probes extenddownwardly from the lower face of the body for simultaneously engaging alarge number of locations on a semiconductor wafer whose resistivity isto be measured. Thus, multiple resistivity readings can be taken at thesame time rather than just a relatively few readings as would ordinarilybe capable only with a single probe. This eliminates having to rotatethe probe assembly as is the case when using a simple probe.

The present invention further contemplates the use of an improved mountfor a probe head wherein a counterbalanced arm is shiftably mounted onan upright post carried on a base plate, and moving means engagable withthe arm is adapted to raise and lower the arm depending upon thedirection of desired travel of the probe head. The moving means can beoperated electrically, pneumatically, hydraulically or by vacuum. Thecontrol means for the moving means can be operated to assure gentle,even movement of the pins of the probe so that the pins will not damagethe semiconductor wafer to be measured yet a relatively few orrelatively large number of resistivity measurements can be takensimultaneously depending upon the type of probe structure which is used.

The primary object of this invention is to provide improvements in theconstruction of resistivity probes for use with and without gram loadingbars wherein the probes are constructed in a manner to minimizeproduction costs yet assure high reliability and accuracy in makingresistivity measurements yet permit quick replacement of the probes ifdeemed necessary or desirable.

Another object of the present invention is to provide an improved mountfor a resistivity probe wherein greater control of the raising andlowering of the probe can be achieved at minimum costs and with highreliability.

Other objects of this invention will become apparent as the followingspecification progresses, reference being had to the accompanyingdrawings for an illustration of several embodiments of the invention.

IN THE DRAWINGS

FIG. 1 is a front elevational view of a first embodiment of theresistivity probe of the present invention, showing the way in which theprobe can be mounted on a housing which is raised and lowered relativeto a semiconductor wafer whose resistivity is to be measured;

FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a view similar to FIG. 1 but showing another embodiment of theresistivity probe of this invention;

FIG. 5 is a cross-sectional view taken along line 5--5 of FIG. 4;

FIG. 6 is a bottom plan view of a disk carrying a number of angularlydisposed resistivity probes for use in making resistivity measurementsat a large number of locations on a semiconductor wafer;

FIG. 7 is a cross-sectional view taken along line 7--7 of FIG. 6;

FIG. 8 is a side elevational view of the mounting stand for aresistivity probe; and

FIG. 9 is a cross-sectional view taken along line 9--9 of FIG. 8.

A first embodiment of the resistivity probe of this invention is broadlydenoted by the numeral 10 and includes a rigid backing strip 12 ofelectrically nonconducting material, such as a rigid plastic, the stripbeing rectangular to present top and bottom edges 14 and 16 and sideedges 18 and 20. Four electrically conducting pins 22 are bonded to oneface 24 of strip 12 by an epoxy material indicated by numeral 26 (FIG.3). The pins are parallel with each other and project beyond top andbottom edges 14 and 16 of strip 12. The lower end of each pin 22 ispointed as is well known for pins of this type. The upper end of eachpin 22 has a metallic collar 28 in electrical contact therewith, and awire 30 is connected to collar 28 and leads away therefrom forconnection to circuitry for measuring resistivity when the lower ends ofthe pins engage a semiconductor wafer.

Strip 12 and pins 22 form a unitary construction which can be mounted ina housing coupled with elevating means for raising and lowering thehousing and thereby the pins relative to a work-piece, such as asemiconductor wafer beneath the pins. For purposes of illustration,probe 10 is mounted in a housing 32 having a pair of opposed side walls34 and a front wall 36 to present a recess for receiving probe 10 in themanner shown in FIG. 2. For mounting strip 12 to housing 32, a pair ofvertical posts 38 are secured into the housing as shown in FIGS. 1 and 2and depend from a lower surface 40 of the housing which defines theupper boundary of the recess in which probe 10 is disposed. The lowerends of posts 38 having horizontal pins 42 (FIGS. 1 and 2) received invertical slots 43 in respective end margins of strip 12 so that thestrip can move slightly in a generally vertical plane relative tohousing 32. A rubber height bar 44 is mounted on surface 40 and engagesthe upper flat faces of pins 22 to limit the upper movement of probe 10to permit each pin 22 to move vertically a few thousandths of an inch toallow the pin to make point contact with similar gram loading ofadjacent pins 22 if there is an uneven surface or semiconductor waferspikes.

In use, probe 10 is mounted to housing 32 in the manner described aboveor in any other desired manner. Then the housing is connected toelevating means (not shown) which raises and lowers the housing relativeto a semiconductor wafer (not shown) beneath probe 10. When resistivitymeasurements are to be made, housing 32 is lowered so that the lowerends of the pins 22 will contact the wafer at the required locations bymeans of selected individual gram weights for proper pin loading to makethe necessary measurements. After the measurements have been taken, thehousing is raised so that the wafer can be rotated into another locationat which resistivity measurements are to be taken. This procedurecontinues until all of the required resistivity measurements are takenfrom the semiconductor wafer. Then the wafer is replaced by anotherwafer and the above procedure is repeated.

The weight gram loading on the pins can be provided by one or more gramloading bars 47, two of which are shown in FIGS. 1 and 2. Suitablemounts 49 connect the bars to housing 32 and to each other.

Another embodiment of the probe of the present invention is shown inFIGS. 4 and 5 and broadly denoted by the numeral 50. Probe 50 includes apair of spaced, rigid strips 52 and 54 of electrically nonconductingmaterial, such as plastic, which are connected together by rivets 56 orother fasteners for mounting therebetween four pins 58 which are used tomake resistivity measurements in the same way as pins 22 of probe 10mentioned above. Each of strips 52 and 54 have four semi-cylindricalrecesses on the inner face thereof for receiving pins 58. Thesemi-cylindrical recesses of the two strips 52 and 54 mate with eachother so that the pins will be captured by the strips and movableslightly vertically in the recesses when the strips are in the positionsas shown in FIG. 5. Collars 59 on respective pins 58 limit the downwardmovement of the pins since the collars normally engage the upper marginsof strips 52 and 54. The collars are electrically conductive and areused for the same purpose as collars 28.

The width of the strips is less than the lengths of pins 58 so that thepins project above and below the strips as shown in FIG. 4. The lowerends of the pins are pointed so that point contact can be made atvarious locations on a semiconductor wafer when the resistivity is to bemeasured.

Probe 50 can be mounted in any suitable manner, such as in the mannershown in FIGS. 1 and 2 with reference to probe 10. Moreover, the twostrips 52 and 54 may be connected in a manner such that slight movementof pins 58 relative to strips 52 and 54 is allowed to compensate foruneven surface on the wafer whose resistivity is to be measured.However, the upper flat faces of pins 58 will generally engage a heightbar (not shown), such as bar 44 of rubber, to limit upward movement ofthe pins relative to strips 52 and 54.

Another embodiment of the invention is shown in FIGS. 6 and 7 and is tobe used when making multiple resistivity measurements at variouslocations on a semiconductor wafer simultaneously. To this end, adisk-like body 60 has a plurality of angularly disposed slots 62 formedtherein and extending between the opposed flat faces thereof. Forpurposes of illustration, there are six slots 62 and each slot isadapted to receive a probe 64 having pins 66 mounted thereon. Each probe64 can be of the type shown in FIGS. 1-3 or of the type shown in FIGS. 4and 5. The width of each slot 62 will be selected so that it willaccommodate the desired width of the corresponding probes.

The slot 62 and probes 64 are symmetrical about the central axis 68 ofbody 60. The probes have strips 70 to which the pins 66 are coupled andthe strips are cut away at the opposed ends thereof at the lower marginsto present shoulders 72 (FIG. 7) which engage lateral projections 74 toseat the probes in respective slots 62 so that the lower ends of pins 66uniformly project downwardly from the lower face 76 of body 60. A rubberheight bar 78 is in each slot 62 above and in engagement with the upperflat faces of pins 66, and a cover plate 80 is attached to the upperflat face of body 60 and prevents upper movement of the height bars 78.Collars (not shown), such as collars 28 and 58, are coupled with pins 66of each probe 64 to connect electrical leads thereto. Cover plate 80 issecured by fasteners 82 to body 60.

In use, body 60 with probes 64 coupled thereto is secured to elevatingmeans to raise and lower body 60 and thereby the various probes 64relative to a semiconductor wafer beneath the body. When the lower endsof the pins of the various probes engage the wafer, a plurality ofresistivity measurements can be successively made at the variouslocations on the wafer so that the totality of the resistivitymeasurements can be taken in much shorter time than would be required ifa single probe 64 were used because the probe assembly need not berotated as in the case of a single probe. In this way, the wafers can bemore effectively handled and wafer production costs will be reducedproportionately. Gram loading bars can also be used with the probeassembly of FIGS. 6 and 7.

FIG. 8 shows a probe mounting stand for use in raising and lowering oneor more probes for making resistivity measurements. The stand, broadlydenoted by the numeral 90, includes a base plate 92 having an uppersurface 94 provided with a recess 96 therein in which a chuck 98 isadjustably and slidably mounted. The chuck has an upper feat surface 100for supporting a semiconductor wafer 102 whose resistivity is to bemeasured at various locations. Means (not shown) for moving the chuckallows the wafer 102 to move beneath a probe head 104 which includes aprobe 106 having vertical pins for making electrical contact with thewafer. Probe 106 can be of the type shown in FIGS. 1-3 or can be of thetype shown in FIGS. 4 and 5. In the alternative, a multiple probeassembly of the type shown in FIGS. 6 and 7 can be used in lieu of asingle probe 106. If the multiple probe assembly is used, body 60 of theprobe is mounted in any suitable manner on probe head 104 so that themultiple probe assembly will be raised and lowered as probe head 104 israised and lowered. Also, gram loading bars can be used with probe head104 as described about with respect to the embodiments of FIGS. 1-7.

Probe head 104 is secured to one end 108 of a vertically shiftable arm110 projecting through a cross beam 111 rigid to and spanning a pair ofvertical tubes 112, each tube 112 being shiftably mounted on arespective upright post 114 having a lower end 116 threadably mounted inbase plate 92. An adjustable counter weight 116 is mounted near one endof arm 110. Each post 114 has upper and lower adjustable stops 118 forlimiting the upward and downward movements of tubes 112 relative to post114.

Means for raising and lowering arm 110 and thereby tubes 112 includes apower device 117, such as a fluid actuator, carried on base plate 92 andhaving a shiftable arm whose upper end engages the underside of crossbeam 111. Control means (not shown) is provided for device 117 to causearm 110 to be raised.

Means to allow gentle lowering of arm 110 includes a vertical shaft 120having a head 122 on the upper end thereof for normally engaging thelower surface 124 of arm 110. Shaft 120 forms part of a governor orcontrol which allows arm 110 to settle at a controlled rate of speeddepending upon the gram loading of the probe head. The governor can beof any suitable construction, such as electrical, pneumatic, hydraulicor vacuum. For purposes of illustration, shaft 120 is controlledpnuematically and, to this end, shaft 120 has a piston 126 on its lowerend which is received within a cylindrical recess 128 formed in theupper surface 94 of base plate 92. A seal 130 surrounds shaft 120 andseals the upper end of the recess in which piston 126 is disposed yetthe piston can move up and down in the recess. A coil spring 132surrounds shaft 120 and extends between head 122 and seal 130 to biasshaft 120 upwardly. An air inlet 134 is in fluid communication with therecess above piston 126 so that, when air is forced into the recessbelow the piston, the piston is cushioned, causing shaft 120 to beslowly lowered to allow arm 110 and thereby probe head 104 to be gentlylowered. Suitable control structure (not shown) will be provided tocontrol the flow of air into and out of the recess.

In operation, probe head 104 is provided with one or more probes. Forpurposes of illustration, only a single probe 106 of the type shown inFIGS. 1-3 or the type shown in FIGS. 4 and 5 is provided at the lowerextremity of probe head 104. With a wafer 102 on chuck 98, the probehead is lowered by de-actuating device 117 while actuating the controlcircuitry which allows air under pressure to enter the recess belowpiston 126. Thereupon, the weight of arm 110 causes it to be loweredagainst the bias force of spring 132, yet the air below piston 126allows arm 110 and thereby the probe head to be lowered gently and at acontrolled rate until the pins of probe 106 engage the wafer at theproper locations. Then, resistivity measurements can be taken, followingwhich device 117 is actuated so that the probe head is raised slightlyto shift chuck 98 to reposition wafer 102 for making the next set ofmeasurements. This procedure continues until all of the requiredresistivity measurements have been taken from the wafer. Then the waferis removed from the chuck and replaced by another wafer whoseresistivity values are to be measured. If the probe assembly shown inFIGS. 6 and 7 is used, many resistivity measurements can be madesimultaneously to avoid having to rotate the probe pins as required witha single probe head. Chuck 98 does not need to be moved, thereby savingtime in making multiple measurements.

I claim:
 1. A resistivity probe comprising: a rigid, electrically,nonconducting strip having a pair of opposed side edges; and a number ofmetallic pins rigidly secured to one side of the strip and projectinglaterally from said side edges, said strip adapted to be secured to aprobe head with said pins being generally vertical, so that the lowerends of the pins can engage a workpiece whose resistivity is to bemeasured.
 2. A resistivity probe as set forth in claim 1, wherein saidpins are adhesively bonded to said side of the strip.
 3. A resistivityprobe as set forth in claim 1, wherein is included a second strip, andmeans connecting the strips together with the pins mounted therebetween.4. A resistivity probe as set forth in claim 3, wherein each strip has asemi-cylindrical recess on the inner surface thereof for each pin,respectively, the pins being shiftably received in respective recessesof the strips, and including a collar on each pin to limit downwardmovement thereof relative to the strips.
 5. A resistivity probe as setforth in claim 1, wherein is included a housing having a recess providedwith an open bottom, and means coupled to said strip for mounting thesame in said recess with the lower ends of the pins projectingdownwardly from said open bottom.
 6. A resistivity probe as set forth inclaim 5, wherein the housing has an inner surface defining an upperboundary of the recess, and including a resilient bar engaging saidinner surface and the upper ends of the pins, said bar being operable tolimit upward movement of the strip and the pins.
 7. A resistivity probeas set forth in claim 1, and including a gram loading bar coupled withthe pins.
 8. A resistivity probe assembly comprising: a body having apair of opposed faces and a number of angularly disposed slots extendingbetween said faces; a resistivity probe for each slot, respectively,each probe having a rigid, strip and a number of spaced, generallyparallel pins mounted on the strip, the strip and pins of each probebeing in a respective slot with the pins projecting outwardly from oneof the faces of the body; means carried by the body for releasablyretaining the probes in respective slots; and means carried by the bodyand coupled with each pin, respectively for electrically connecting thepin with a circuit externally of the body.
 9. An assembly as set forthin claim 8, wherein said body is cylindrical and said faces are flat,said body having a resilient height bar in each slot, respectively, eachheight bar engaging the inner ends of the pins of the respective probe.10. An assembly as set forth in claim 8, wherein the body is cylindricaland provided with a central axis, the slots bieng generally symmetricalabout said central axis.